1. Field of the Invention
The present invention relates generally to power detection in a multiple frequency band transmission system, and specifically to a single wide frequency range coupler and detector pair for detecting the transmitted power of a multiband telephone.
2. Description of Related Art
Mobile phones have recently gained widespread use throughout the world. Mobiles phones communicate with a base station serving a predetermined area or cell. Each base station has a limited bandwidth within which to operate, depending upon the particular transmission technique utilized by the base station. This limited bandwidth is separated into a plurality of channels frequency-spaced evenly from one another, where these channels are used by the mobile phones within that base station""s transmission area. Each base station may only handle a limited number of phones equal to the number of channels and time-slots on those channels provided by that base station. Therefore, the frequency spacing between channels is minimized in order to maximize the number of channels supported by the operating bandwidth of the base stations.
In order to prevent interference between signals on two adjacent channels, the power levels of the signals transmitted by the phones must be precisely controlled. As the mobile phones move around within a base station""s cell, the power levels received at the base station will change. For instance, the power level received at the base station will increase as the phone moves closer to the base station if the signal continues to be transmitted at the same power level. Interference between adjacent channels will occur if the power level of a signal received at the base station from one of the phones is too large. Therefore, the systems must constantly monitor and adjust the transmission power levels as the phones move within a base station""s cell to avoid interference between channels. Each phone includes a power amplifier controller (PAC) which controls a power amplifier for the transmitted signal. The PAC in each phone adjusts the transmitted power level to maintain a minimum interference between the signals received at the base station on all channels at a constant level. A certain amount of error correction is transmitted with each signal by the system, wherein the amount of error correction is predetermined based upon the constant interference level.
The capacity of base stations in highly populated areas can become saturated during time periods of high use. Mobile phones currently operate as single band phones, where the transmitted signal frequency is within the bandwidth of a base station operating on the same transmission method as the mobile phone. There is a need for mobile phones to operate with dual band transmissions to increase system capacity, so that the systems could choose between two transmission frequencies depending upon which bandwidth is less saturated and could achieve a better signal quality. A dualband phone requires two transmitters, one for each frequency band. Since the power levels of the signals transmitted by a mobile phone must be constantly monitored and adjusted, dualband mobile phones must also include a power detector for each transmitter. However, requiring two power detectors in a dualband phone adds to the cost, complexity, and size of the dualband phone. Most mobile phones are designed to be lightweight and portable, so that they may be easily carried on the person using the mobile phone, such as in their pocket or purse. It is therefore critical to design a mobile phone to be as small as possible, thus requiring the number of components to be minimized.
There is a need for a multiband system which selects between one of the possible frequency bands at which to transmit a signal based upon the strength and quality of the transmitted signal received at a base station. Moreover, there is a need for a multiband phone having a single power detector to detect the power level of the transmitted signal at multiple possible frequency bands, regardless of which frequency band is selected for transmission.
It is a primary object of the present invention to overcome the aforementioned shortcomings associated with the prior art.
Another object of the present invention is to provide a multiband phone which selects between one of a plurality of frequency bands to transmit a signal based upon the strength and quality of the transmitted signal received at a base station.
Yet another object of the present invention is to provide a multiband phone having a wide frequency range coupler and detector pair for measuring the power of the transmitted signal, regardless of which frequency band is selected for transmission.
A further object of the present invention is to provide a wide frequency range coupler and detector pair whose design parameters are adjusted to provide the optimal balance for power detection between the various individual frequencies transmitted by the multiband phone.
These as well as additional objects and advantages of the present invention are achieved by providing a multiband phone having multiple transmitters, each transmitter capable of transmitting a signal in a different frequency band. The multiband phone includes multiple power amplifiers, where each power amplifier amplifies the power of a signal transmitted at a different frequency band. A power amplifier controller is provided for controlling the amount of amplification performed by the power amplifiers. A power amplifier switching device is connected to the power amplifier controller for switching the connection of the power amplifier controller between the multiple power amplifiers, so that only one of the power amplifiers is connected to the power amplifier controller at one time. The multiband phone further includes a processing device which monitors the quality and strength of the received signal transmitted by various base stations in the transmission region of the multiband phone. The base stations also monitor the quality and strength of the signals they receive from the multiband phone. The base stations instruct the processing device to control the power amplifier switching device to switch its connection between the power amplifiers based upon a determination of which frequency band provides the optimal balance between signal quality and signal strength, and the multiband phone then transmits within the selected frequency band.
The processing device includes a stored predetermined relationship between signal strength and a voltage driving the power amplifiers, where the processing device instructs the power amplifier controller to adjust the voltage driving the connected power amplifier according to the desired signal strength. The system monitors the quality and strength of the received signal during each duty cycle and the system selects which one of the multiple power amplifiers should be connected to the power amplifier controller for each duty cycle.
The multiband phone also includes a single power sensing device connected to the output of the all of the power amplifiers through a switching device, where the switching device connects the power sensing device to the particular power amplifier selected for transmission. The power sensing device then measures the power of the signal transmitted, and the measured power of the transmitted signal is fed back to the power amplifier controller. The power amplifier controller adjusts the voltage driving the power amplifier connected thereto based upon any difference detected between the desired power output by the connected power amplifier and the measured power of the signal output by the connected power.
The power sensing device includes a wide frequency range directional coupler and a wide frequency power detector capable of effectively measuring the power of any of the desired frequencies selected for transmission by the multiband phone. The performance of the wide frequency range coupler and power detector is adjusted for the specific transmission frequencies utilized by the multiband phone to provide desired performance characteristics over all of the multiple frequency bands. This enables a single power detector to be used for the multiple frequency bands capable of being transmitted by the multiband phone.
The multiband phone further includes a transmitting antenna connected to the output of the power amplifiers. The design parameters of the directional coupler are chosen such that a maximum isolation is provided between the detector and the antenna to minimize signals reflected back from the antenna. Thus, the measured output power signal fed back to the power amplifier controller will only be indicative of the power of the signal transmitted to the antenna and will not include any extraneous signals reflected from the transmitting antenna.